Advanced multi-shouldered fixed bobbin tools for simultaneous friction stir welding of multiple parallel walls between parts

ABSTRACT

A multi-shouldered friction stir welding tool comprises an exterior threaded solid pin having a diameter and a length; a shoulder having a threadless inner diameter slightly larger than the diameter of the exterior threaded solid pin and at least one substantially radial threaded set screw hole; an monolithic shoulder-shank having a threadless inner diameter slightly larger than the diameter of the exterior threaded solid pin and at least one substantially radial threaded set screw hole; a pair of locking nuts having a threadless outer diameter and a threaded inner diameter operably compatable with the exterior threaded solid pin, wherein the shoulder and the monolithic shoulder-shank are capable of slidable engagement with the exterior threaded solid pin along the length of the exterior threaded solid pin to set a space slightly larger than a thickness of a work piece to be welded.

CROSS-REFERENCED APPLICATIONS

The present invention claims benefit of U.S. Non-Provisional applicationSer. No. 12/048,696, entitled “ADVANCED MULTI-SHOULDERED FIXED BOBBINTOOLS FOR SIMULTANEOUS FRICTION STIR WELDING OF MULTIPLE PARALLEL WALLSBETWEEN PARTS” filed on Mar. 14, 2008, which is incorporated herein.

BACKGROUND OF THE INVENTION

The present invention relates to a multi-shouldered friction stirwelding bobbin tool for friction stir welding and, more particularly,the present invention relates to using a multi-shouldered friction stirwelding tool for simultaneous friction stir welding of a plurality ofparallel joints between components having parallel portions.

The Friction Stir Welding (FSW) process is a solid-state based joiningprocess, which makes it possible to weld a wide variety of materialsalloys (aluminum, copper, stainless steel, etc.) to themselves andcombinations (e.g. 6XXX/5XXX, 2XXX/7XXX, etc.) The joining is effectedby a rotating FSW tool, which is forced into the joining area to heat itby friction and thus “plasticizes” the parts about it. Plasticizedmaterial flows around the axis of the rotating FSW tool, and theplasticized regions coalesce into sound metallurgical bonds.

In one embodiment, the present invention discloses a multi-shoulderedfriction stir welding tool comprising an integral shank-pin unit havinga plurality of pin portions on the shank-pin unit, where the pluralityof pin portions for plunging into a plurality of joints to perform afriction stir welding operation on the corresponding plurality of jointsand, where a shank portion of the shank-pin unit is for attachment to anoptional axial tension rod, a plurality of friction stir weldingmodules, each of the friction stir welding modules comprising a pair ofshoulders that is connected to the shank-pin unit where each shoulderhas a distal end and a proximal end, where the proximal end of eachshoulder faces the pin portion of the shank-pin unit, whereby theshoulder and pin(s) rotate in unison, and a pair of split collars or apair of nuts that is connected to the shank-pin unit and faces thedistal end of each shoulder, where the plurality of friction stirwelding modules are connected to each other whereby the modules rotatein unison to simultaneously make a plurality of parallel welds.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a multi-shoulderedfriction stir welding tool for simultaneous friction stir welding of aplurality of parallel joints between components having parallelportions. The multi-shouldered friction stir welding tool comprising anintegral shank-pin unit having a plurality of pin portions on theshank-pin unit, where the plurality of pin portions for driving into aplurality of joints to perform a friction stir welding operation on thecorresponding plurality of joints and, where a shank portion of theshank-pin unit is for attachment to an optional axial tension rod, aplurality of friction stir welding modules, each of the friction stirwelding modules comprising a pair of shoulders that is connected to theshank-pin unit where each shoulder has a distal end and a proximal end,where the proximal end of each shoulder faces the pin portion of theshank-pin unit, whereby the shoulder and pin(s) rotate in unison, and apair of split collars or a pair of nuts that is connected to theshank-pin unit and faces the distal end of each shoulder, where theplurality of friction stir welding modules are connected to each otherwhereby the modules rotate in unison to simultaneously make a pluralityof parallel welds.

In one embodiment, the axial tension rod is disposed within the shankportion of the multi-shouldered friction stir welding tool shank-pinunit. In another embodiment, the shank-pin unit contains a loading meansfor placing the axial tension rod in tension and the shank-pin incompression.

In a further embodiment, the shank-pin unit has threadless ends with atleast two flats along the length of the shank-pin unit. In anotherembodiment, each shoulder has an opening to facilitate contact withthreads on the shank-pin unit.

In yet another embodiment, each split collar has a threaded outerdiameter and a threaded inner diameter that is connected to theshank-pin unit by threading the outer diameter of the collar ontothreads on an inner diameter of the shoulder and threading the innerdiameter of the collar onto threads on an outer diameter of theshank-pin unit. In another embodiment, each split collar is furthertightened against or connected to the shank-pin unit by screws.

In another embodiment, the shank-pin is made of a solid rod.

In a further embodiment, each nut has a threaded outer diameter and athreaded inner diameter that is connected to the shank-pin unit bythreading the outer diameter of the nut onto threads on an innerdiameter of a shoulder and threading the inner diameter of the nut ontothreads on an outer diameter of the shank-pin unit. In anotherembodiment, each nut is further tightened against or connected to theshank-pin unit by screws. In another embodiment, each nut is furtherconnected to the shank-pin unit by jam nuts.

In a further embodiment, the shoulder may be a drive shank with anintegrated shoulder.

In yet another embodiment, the loading means for placing the axialtension rod in tension and the pin-shank in compression is a bearingdisposed in a shank-pin unit end for disengaging and relieving thetorque experienced by the pin portions of the shank-pin unit during thefriction stir welding operation.

In yet another embodiment, the distal end of the shoulder and thethreaded outer diameter of the collar create a small pocket to preventthe plasticized material from flowing out of the joint.

In yet another embodiment, the present invention provides a method offriction stir welding a plurality of parallel joints simultaneouslyusing at least one multi-shouldered friction stir welding tool. In afurther embodiment, the two multi-shouldered friction stir welding toolsare simultaneously driven by a rotation-splitting transmission system orby two synchronized Servo controlled motors.

Accordingly, it is one embodiment of the invention to provide amulti-shouldered friction stir welding tool for simultaneous frictionstir welding of a plurality of parallel joints between components havingparallel portions.

It is another embodiment of the invention to provide a method offriction stir welding a plurality of joints simultaneously using atleast one multi-shouldered friction stir welding tool as claimed herein.

These and other further embodiments of the invention will become moreapparent through the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is made to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is an elevational view of one embodiment of a multi-shoulderbobbin type friction stir welding tool for simultaneously welding twoparallel joints in accordance with an embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of one embodiment of the multi-shoulderbobbin type stir welding tool of FIG. 1 with an internal tension rod;

FIG. 3A is an exploded view of one embodiment of the drive shankassembly end of the multi-shoulder bobbin type friction stir weldingtool of FIG. 1;

FIG. 3B is a cross-sectional view of one embodiment of an assembleddrive shank assembly end with a thrust bearing for disengaging thetension rod from the torsion experienced by the pin shank of themulti-shoulder bobbin type friction stir welding tool in accordance withanother embodiment of the present invention;

FIG. 3C is an exploded view of one embodiment of the bottom end of thethrust bearing end of the multi-shoulder bobbin type friction stirwelding tool of FIG. 1;

FIG. 4A is an elevational view of one embodiment of the integralshank-pin unit used in the multi-shoulder bobbin type friction stirwelding tool in accordance with an embodiment of the present invention;

FIG. 4B is a perspective view of one embodiment of the threadless bottomend of shank-pin unit of FIG. 4A;

FIG. 4C is a front view of one embodiment of the threadless top end ofshank-pin unit of FIG. 4A;

FIG. 4D is a view of one embodiment of the threads on pins 12 ofshank-pin unit of FIG. 4A;

FIG. 5A is an elevational view of one embodiment of the integralshank-pin unit used in the multi-shoulder bobbin type friction stirwelding tool in accordance with another embodiment of the presentinvention;

FIG. 5B is a front view of one embodiment of a shoulder used on theintegral shank-pin unit of FIG. 5A in accordance with an embodiment ofthe present invention;

FIG. 5C is a front view of one embodiment of one end of shank-pin unitof FIG. 5A;

FIGS. 6A and 6B are elevational views of one embodiment of assembling ashoulder onto the shank-pin unit with a split collar in accordance withan embodiment of the present invention;

FIGS. 7A, 7B and 7C are elevational views of one embodiment ofassembling a shoulder onto the shank-pin unit with a split collar inaccordance with another embodiment of the present invention;

FIG. 8 is a cross-sectional view of one embodiment of a friction stirwelding module in accordance with an embodiment of the presentinvention;

FIG. 9 is an elevational view of one embodiment of two opposingmulti-shoulder bobbin type friction stir welding tools forsimultaneously welding two parallel joints each in accordance with anembodiment of the present invention;

FIG. 10 is a cross-sectional view of one embodiment of the twomulti-shoulder bobbin type stir welding tool of FIG. 9 with an internaltension rod;

FIG. 11 is a perspective view of one embodiment of two opposingmulti-shoulder bobbin type friction stir welding tools of FIG. 10simultaneously welding two parallel joints each in accordance with anembodiment of the present invention;

FIGS. 12A, 12B, 12C and 12D are perspective views of one embodiment oftypes of torque-splitting transmission used to simultaneously andsynchronically drive the two multi-shoulder bobbin type friction stirwelding tools in accordance with an embodiment of the present invention;

FIG. 13 is a perspective view of one embodiment of two Servo drivenmotors used to simultaneously and synchronically drive the twomulti-shoulder bobbin type friction stir welding tools in accordancewith another embodiment of the present invention;

FIG. 14 is a cross-sectional view of one embodiment of the use of adouble ended split collar in accordance with another embodiment of theinvention; and

FIGS. 15A and 15B are elevational views of one embodiment of assemblinga shoulder and a driving shank onto the shank-pin unit with a captureadjusting nut in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides multi-shouldered fixed bobbin tools thatafford simultaneous friction stir welding of multiple parallel jointsbetween parts, such as sheet, plate a flange or a web, a planner portionof an extrusion, a planner portion of a casting, etc.

in the discussion which follows, directional terms such as “upper”,“lower”, “top”, “bottom”, etc., apply relative to welding setupsoriented with the bottom end of the FSW tool at the bottom and the shankend at the top. The terms “distal” and “proximal” are also used. Distalhas the meaning of farthest from the pins of the FSW tool, proximalmeans nearer.

In one embodiment, the present invention discloses a multi-shoulderedfriction stir welding tool comprised of an integral shank-pin unithaving a plurality of pin portions on the shank-pin unit, where theplurality of pin portions for plunging into a plurality of joints toperform a friction stir welding operation on the corresponding pluralityof joints and, where a shank portion of the shank-pin unit is forattachment to an optional axial tension rod, a plurality of frictionstir welding modules, each of the friction stir welding modulescomprising a pair of shoulders that is connected to the shank-pin unitwhere each shoulder has a distal end and a proximal end, where theproximal end of each shoulder faces the pin portion of the shank-pinunit, whereby the shoulder and pin(s) rotate in unison, and a pair ofsplit collars or a pair of nuts that is connected to the shank-pin unitand faces the distal end of each shoulder, where the plurality offriction stir welding modules may be directly or indirectly connected toeach other whereby the modules rotate in unison to simultaneously make aplurality of parallel welds. For example, the plurality of friction stirwelding modules may be connected laterally and rotationally throughflexible links.

In one embodiment, to friction stir weld with a multi-shouldered fixedbobbin tool: a) multiple parallel joints (e.g. 2, 4), b) relativelythick walls (2.5 cm), and c) tough/strong alloys (e.g. 7085), the toolmust be extra strong to resist the severe cyclic bending and twisting atits pins during welding. To prevent the intense cyclic bending andtwisting during welding of multiple parallel joints of the FSW tool, thepresent invention advances the concept of combining the use ofcompression loading of the pins, between the shoulders, with the aid ofan internal tension member and also the concept of an integral pin/shankensemble with a self-locking shoulder and a split collar threaded ontothe pin/shank ensemble.

In one embodiment, FIG. 1 shows a multi-shoulder bobbin type frictionstir welding tool 10 (“FSW tool”) according to the present invention. Inone example, FSW tool 10 is for making two parallel welds simultaneouslyand includes an integral shank-pin unit 11 which may be held in a chuckor collet of a friction stir welding machine. In one example, FSW tool10 also includes two pins 12 with each having a left shoulder 13 and aright shoulder 14 surrounding pins 12. Each left shoulder 13 and rightshoulder 14 has a split collar 16. In yet another example, split collars16 firmly secure each shoulder 13 and 14 to shank-pin unit 11. At oneend of FSW tool 10 is a drive shank 17 where FSW tool 10 is attached tothe friction stir welding machine collet (not shown). At the end of thedrive shank 17, the mechanism that puts the tension member in tensionand thus putting the pin into compression, is located. This mechanism iscomprised of a race/support 21 and a collar retainer 22 underneath whichis located a split collar 16, a washer 27, and a plurality of discsprings 23 therebetween as shown in FIG. 3A. Race/support 21 and discsprings 23 may, for example only, be a Belleville™ race/support and aBelleville™ disc springs, respectively. At the other end of FSW tool 10is a thrust bearing retainer 18. Washer 24 prevents ends of shank-pinunit 11 from pushing against bearing 26.

In another embodiment, split collars 16 are replaced with nuts that arealso called capture adjusting nuts. In a further embodiment, FSW toolmay be for making more than two parallel welds.

In the following discussion, it is presumed that FSW tool 10 is to berotated clockwise. In this case, both shoulders 14 are right handedshoulders, that is to say, have clockwise inner diameter threads andboth of the shoulders 13 are left handed shoulders, that is to say, theyhave counterclockwise inner diameter threads.

As will be discussed in more detail below, each pin 12 has at least oneflat area 34 that exists across the two types of threads as shown inFIG. 4D. These flats 34 prevent shoulders 13 and 14 from rotating duringthe engagement with split collars 16 and during friction stir welding.As shown in FIGS. 6A and 6B, shoulders 13 and 14 are affixed toshank-pin unit 11 through split collars 16, where each half of thesesplit collars 16 has threads on an inner diameter 16 b and an outerdiameter 16 a, while each of the shoulders 13 and 14 has threads on aninner diameter 13 b and 14 b, respectively. Shoulders 13 and 14 areaffixed to the shank-pin unit 11 by turning and threading in splitcollars 16, so that their inner diameter 16 b is threaded onto shank-pinunit 11 and their outer diameter 16 a is threaded into the innerdiameter 13 b and 14 b of shoulders 13 and 14. When split collars 16 arejammed-threaded against the threads on an outer diameter 11 a ofshank-pin unit 11 and inner diameter 13 b and 14 b of the shoulders,shoulders 13 and 14 get located and fixed along shank-pin unit 11.

Here, right hand shoulder 14 that is more towards the right is attachedto shank-pin unit 11 having a shank portion and a pin portion 12 a asshown in FIG. 4D. Right hand shoulder 14 that is more towards the leftis attached to the same shank-pin unit 11 which includes pin portion 12a.

Similarly, left handed shoulder 13 is attached to shank-pin unit 11having a shank portion and a pin portion 12 b as shown in FIG. 4D. Lefthanded shoulder 13 that is more towards the right is attached to thesame shank-pin unit 11 which includes pin portion 12 b.

The threads on pin portions 12 a are left handed threads, so thatplasticized material is urged from a merge point 33 of pin portion 12 aand pin portion 12 b towards the scroll shoulders when FSW tool 10 isrotated in a clockwise direction. Likewise, the threads on pin portions12 b are right handed threads so that plasticized material is urgedtoward the corresponding shoulder when FSW tool 10 is so rotated. Also,split collars 16 firmly secure each shoulder 13 and 14 to shank-pin unit11 in the correct place. Moreover, in one embodiment, optionally screwsmay be used to connect the two halves of split collar for extra securityas shown in FIG. 7B.

In one embodiment, the cross-sectional view of FSW tool 10 is shown inFIG. 2. Here, an axial tension rod 19 is disposed along the entirelength of the shank-pin unit 11. When this rod 19 is put under tension,it puts the shark-pin under compression, parts of which are the pinsbetween shoulders 14 and 13.

In one embodiment, FIG. 3A shows an exploded view of drive shankassembly of FSW tool 10. In one embodiment, FIG. 3B shows across-sectional view of an assembled drive shank assembly end 40 withthrust bearing 26. In one embodiment, FIG. 3C shows a bearing race 24and thrust bearing retainer 18 holding thrust bearing 26 in place. Inanother embodiment of the present invention, thrust bearing 26 may belocated at the drive shank end of the FSW tool as shown in FIG. 3B.Here, thrust bearing 26 is located between race/support 21 and collarretainer 22. Race/support 21 may, for example only, be a steel washer.

In one embodiment, one of the purposes of the thrust bearing 26 alsocalled the swivel portion is to disengage and relieve the internaltension rod from the torsion experienced by the pins during the FSWoperation.

In another embodiment, the shank-pin unit is a solid rod without aninternal tension rod. In this case, a thrust bearing is not needed inthe FSW tool.

FIG. 4A shows a hollow shank-pin unit 11 to possibly accommodate aninternal tension rod in accordance with one embodiment of the presentinvention. Shank-pin unit 11 has a threadless top end 28 and athreadless bottom end 29. Threadless top end 28 has a drive collartorque with four flats 28 a (FIG. 4B) for engaging with drive shank 17(FIG. 1). In one embodiment, flats 28 a are on the top, bottom, left andright side of threadless top end 28 as shown in FIG. 4B. There is also acollar stop feature 36, which is comprised of the ends of the four flats28 a, against which the end face of the shank rests.

FIG. 4C shows the front view of threadless bottom end 29 with toolshoulder torque flats 29 a in accordance with one embodiment of thepresent invention. There are two opposite flats 29 a on threadlessbottom end 29 for engaging with a “swivel” mechanism, when it isseparate from an internal tension rod 19 with a tensioning mechanism,based on washers 27 (FIG. 3A) which may, for example only, be Bellville™washers on the other end of shank-pin unit 11.

In one embodiment, FIG. 4D is a view of the alternating left handthreads 12 b and right hand threads 12 a on shank-pin unit 11 with mergepoint 33 between the two types of threads. A flat area 34 exists acrossthe two types of threads as shown in FIG. 4D. In one embodiment,shank-pin unit is threaded with opposite threads along its entirelength. In another embodiment, shank-pin unit is threaded with oppositethreads only where the pins are located and the threads are machinedflat 120 or 90 degrees apart along the entire length of the pin-shank.These flats prevent the shoulders from rotating during the engagementwith the split collars.

FIG. 5A shows another embodiment where a shank-pin unit 41 is solid.FIG. 5B shows the flats that are machined into the opening 14 a ofshoulder 14 to be used on the FSW tool to engage with correspondingflats 42 a on shank-pin unit 41 to prevent the rotation of shoulder 14during welding. This tight fit between the opening 14 a of shoulder 14and an end 42 of shank-pin unit 41 reduces plasticized material frompropagating or extruding into the threaded connection between the innerdiameter of shoulder 14 and the outer diameter of shank-pin unit 41,which facilitates the ease of assembly, disassembly and adjustment oflocation of each shoulder.

The opening on each of the shoulders is designed to slip over the threadof the shank-pin unit and engage with flats during the weldingoperation. This opening in conjunction with the thread on the shoulder'sinner diameter allow the placement of each shoulder, exactly where itneeds to be along the shank-pin assembly and firmly secured to theshank-pin unit with the aid of the split collar.

In one embodiment, FIG. 6A shows how split collar 16 is engaged withshoulder 14. Here, split collar 16 has an outside diameter 16 a and aninside diameter 16 b that is threaded. Split collar 16 is comprised oftwo halves. Once the two halves of split collar 16 are assembled it isscrewed into the back end of shoulder 14. The threads on an innerdiameter 14 b (shown in FIG. 8) of shoulder 14 contact the threads onoutside diameter 16 a of split collar 16. The threads on the innerdiameter 16 b of split collar 16 are threaded on an outer diameter 11 a(shown in FIG. 8) of shank-pin unit 11. Split collar 16 is rotated toengage shoulders 13 and 14, as shown by arrows A in FIG. 6B, to theouter diameter threads on the shank-pin 11. Optionally, in anotherembodiment, the two halves of split collar 16 may be further secured bythe used of a set of screws 47 as shown in FIG. 7B.

FIGS. 7A, 7B and 7C show assembling shoulder 14 onto the shank-pin unit11 where a split collar 16 is secured to the shank-pin unit with a setof screws 47 in accordance with an embodiment of the present invention.First, shoulder 14 is slipped over shank-pin 11 where it should besecured for welding relative to the pin (between shoulders 13 and 14).Then, two halves of split collar 16 are assembled and threaded aroundshank-pin unit 11 and the distal end of shoulder 14. Optionally, inanother embodiment, two screws 47 are then inserted and tightened tosecure split collar 16 to shank-pin unit 11 as shown by arrows B.

In one embodiment, FIG. 8 shows a cross-sectional view of a frictionstir welding module 48 of FSW tool 10 that shows the relationshipbetween shank-pin unit 11, shoulders 13 and 14 and split collars 16.Here, a pocket 49 for the accumulation of plasticized material fromfriction stir welding is shown between the back of shoulder 14 and thefront of split collar 16. There is also an optional tapered pipe threadinterface 37 to aid in the locking of split collar to shank-pin unit.

The loading mechanism of the tension rod and the thrust bearing/swivelportion may be placed on the ends of FSW tool in a variety of ways. Inone embodiment, the tension rod loading mechanism may be combined withthe swivel portion on drive end of the FSW tool. In another embodiment,the loading mechanism of the tension rod and the swivel portion may beon the drive end of the FSW tool but be separate from each other. Infurther embodiment, the loading mechanism may be on the drive end whilethe swivel portion is on the other end of the shank-pin unit.

In one embodiment, FIG. 9 shows two opposing multi-shoulder bobbin typefriction stir welding tools 50 for simultaneously welding two paralleljoints each.

In one embodiment, FIG. 10 shows the cross-sectional view of FIG. 9 thatshows two opposing multi-shoulder bobbin type friction stir weldingtools 50 for simultaneously welding two parallel joints each withinternal tension rod 19. In another embodiment, shank-pin unit may besolid so there is no internal tension rod disposed along the entirelength of the shank-pin unit.

In one embodiment, FIG. 11 shows two opposing multi-shoulder bobbin typefriction stir welding tools 50 simultaneously welding two paralleljoints each between workpieces 53 and 54.

There are many different types of torque-splitting transmissions thatmay be used to simultaneously and synchronically drive twomulti-shoulder bobbin type friction stir welding tools. FIGS. 12A, 12B,12C and 12D show examples of types of torque-splitting transmission thatcan be used to simultaneously and synchronically drive the twomulti-shoulder bobbin type friction stir welding tools. Further, inanother embodiment, the two multi-shoulder bobbin type friction stirwelding tools may be driven simultaneously and synchronically by twoServo driven motors as shown in FIG. 13.

One embodiment 100 of the present invention, a cross-sectional viewshown in FIG. 14, provides for the placement of two monolithicpin-shoulder units 52A, 52B in back-to-back orientation.Multi-shouldered FSW tool 100 consists of two different pairs ofmonolithic (i.e. not split) shoulder-pin units 52A, 52B that can becylindrical and hollow (e.g., having a bore-hole 62 therethrough) beingcoupled together in opposing orientation (e.g., shoulder back 63 toshoulder back 64) by coupler 51. Coupler 51 has outer diameter (OD) 60with threaded end portions 66 and 68, which are threaded into the innerdiameter (ID) threads 70 and 72 of shoulder portions 52C, 52D ofmonolithic shoulder-pin units 52A, 52B, respectively, to form upper FWStool part 100A of FWS tool 100. OD/ID thread pairs 66, 70 and 68, 72 aredesigned with opposing threads (e.g., one set being left-hand threadsand the other set being right-hand threads) to form a self-lockingmechanism (i.e. counter threads tighten during operation) as tool 100rotates during the friction stir welding process. Monolithicshoulder-pin unit 52A is a monolithic component comprising two shoulders74, 76 and a hollow pin 80 disposed therebetween to connect shoulders74, 76. Hollow pin 80 has a predetermined length L that defines themaximum work piece thickness T of work piece 53 (shown in phantom view)that can be welded. Hollow pin length L must be slightly larger thanwork piece thickness T to allow plastisized metal to flow around hollowpin 80.

Monolithic shoulder-pin unit 52B is a monolithic part comprisingshoulder portion 52D with a single shoulder 78 and a threaded innerdiameter 72, and a hollow pin 25 with a threaded outer diameter end 25A.Threaded outer diameter end 25A can be inserted into bore 17A ofmonolithic shoulder/shank 17 and threaded into threaded inner diameterend portion 17B of bore 17A to form lower FSW tool part 100B of FWS tool100. Threads of outer diameter end 25A and inner diameter end portion17B are designed such that a predetermined rotation in degrees orangular displacement of shoulder/shank 17 will longitudinally advancemonolithic shoulder-pin unit 52B into or out of shoulder/shank 17 apredetermined linear distance to set gap G between shoulder 78 andshoulder portion 82 of shoulder/shank 17. This arrangement of monolithicpin-shoulder unit 52B with threaded end 25A and threaded inner diameterend portion 17B of bore 17A of shoulder/shank 17 provides for a gap orpin working surface control mechanism such that gap G can be equal to,greater than, or less than length L of pin 80 of monolithic pin-shoulderunit 52A. Therefore, the present invention is not limited tosimultaneously welding parallel work pieces of the same thickness.

A further embodiment of the above mentioned FSW tool 100 can includetightening nut 84 with threaded inner diameter (ID) 84A threaded ontoouter diameter end 25A and into an abutting relationship withshoulder/shank end 17C to rotationally lock shoulder/shank 17 whereoperational torsional loading causes gap G to vary during FSW.

Other embodiments (not shown) of the tool 100 comprising three (3) ormore pin sections can be created with a series of couplers 51 threadedinto threaded inner diameter 52F (not shown) of distal end 52E ofmonolithic shoulder-pin unit 52A.

Another embodiment of FSW tool 100 can include tension rod 19 (discussedin detail above) inserted into distal end 52E of monolithic shoulder-pinunit 52A to pass through bore-holes 62 of monolithic shoulder-pin units52A, 52B to extend proximate end 19A of tension rod 19 throughshoulder/shank end 17C and end 84B of tightening nut 84 (when tighteningnut 84 is used). Tension rod 19 can induce a compressive assembly loadon to the entire FSW tool 100 such that the alternating stress range ofthe working surfaces, for example shoulders 74, 76, 78 and pins 62, ofthe FSW tool 100 are lowered to impart extra durability (e.g., low cyclefatigue, high cycle fatigue, and crack propagation) into tool 100 bymaking it more resistant to a combination of cyclic flexing andtorsional type loading. As shown in FIGS. 3A and 3B and discussed above,tension rod 19 can to put under tension at shoulder/shank end 17C ofshoulder/shank 17. The tensioning mechanism comprises a race/support 21and a collar retainer 22 underneath which is located a split collar 16,a washer 27, and a plurality of disc springs 23 therebetween as shown inFIG. 3A. Race/support 21 and disc springs 23 may, for example only, be aBelleville™ race/support and a Belleville™ disc springs, respectively.

To decouple the tension rod 19 from the torsional-type “twisting” of thetool's hollow pins, a swivel mechanism 90 is placed at the distal end100C of tool 100 opposing the proximal end 100D at which the Bellville™washers 23 based rod-tensioning mechanism is located. Swivel mechanism90 comprises thrust bearing retainer 18 holding thrust bearing 26 inplace. Thrust bearing retainer 18 includes a recess 92 to seat distalend 94 of tension rod 19. Distal end 94 has diameter D1 larger thandiameter D2 of shaft 96 of tension rod 19. One of the purposes of thrustbearing 26 is to disengage and relieve the internal tension rod 19 fromthe torsion experienced by the pins during the FSW operation when thetorsional load exceeds fatigue capability of the shoulders 74, 76 or pin80 of the dual shoulder monolithic shoulder-pin unit or the shoulder 78or pin 25 of the single shoulder monolithic shoulder-pin unit.

In one embodiment, FIGS. 15A and 15B show how capture adjusting nut 56is attached to shoulder 14. Here, capture adjusting nut 56 has athreadless outside diameter 56 a and a threaded inside diameter 56 b.The threads on the inner diameter 56 b of capture adjusting nut 56 arethreaded on an outer diameter 41 a of shank-pin unit 41 and at the sametime it is inserted into the threadless inner diameter 14 b 1 ofshoulder 14 as shown in FIG. 1513. The outside diameter of captureadjusting nut 56 has a smooth groove 58 a that is designed to “receive”the ends of screws 58. Screws 58 may freely turn/slide in groove 58 a,as capture adjusting nut 56 is turned along pin 41 and thus movingshoulder 14 with it longitudinally along the axis of pin 41. Then screws58 are screwed into substantially radial set screw holes 99A in the wallof shoulder 14, to the point where the screw ends are placed in smoothgroove 58 a.

FIGS. 15A and 15B also show how capture adjusting nut 57 is attached toa drive shank with integrated shoulder 55. Here, capture adjusting nut57 has a threadless outside diameter 57 a and a threaded inside diameter57 b. Capture adjusting nut 57 is threaded over outside diameter 41Athread on pin 41 and at the same time it is inserted into the threadlessinner diameter 55A of drive shank-shoulder 55 as shown in FIG. 15B. Theoutside diameter of capture adjusting nut 57 has a smooth groove 58 athat is designed to “receive” the ends of screws 58. Screws 58 mayfreely turn/slide in groove 58 a, as capture adjusting nut 57 is turnedalong pin 41 and thus moving shank-shoulder 55 with it longitudinallyalong the axis of pin 41. Then screws 58 are screwed into substantiallyradial set screw holes 99B in the wall of the shank-shoulder 55, to thepoint where the screw ends are placed in smooth groove 58 a.

This arrangement of adjustable drive shank-shoulder 55 and shoulder 14provides for varying space S between the two shoulders, 14 and 55 thatdefines the length of the working surface of the pin portion by rotatingthe capture adjusting nut 57, which moves along the threaded outsidediameter 41A of shank-pin unit 41, while “moving with it” theshank-shoulder 55, whose internal diameter is threadless and is attachedto adjusting nut 57 through two pins, 58, that slide within groove 58 aon the outside diameter of nut 57, as shown in arrow C in FIG. 15B.Space S is slightly larger than the thickness T of the work pieces(shown in phantom view) to allow plastisized metal to flow around pinworking surface 98. Threaded tightening nuts 59 can be threaded onoutside diameter 41A on both ends of shank-pin unit 41 and abuttedagainst capture adjusting nuts 56, 57 to rotationally lock shoulder 14and integrated shoulder 55, respectively, where operational torsionalloading causes space S to vary during FSW.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof.

1-6. (canceled)
 7. A multi-shouldered friction stir welding tool comprising: an exterior threaded solid pin having a diameter and a length; a shoulder having a threadless inner diameter slightly larger than the diameter of the exterior threaded solid pin and at least one substantially radial threaded set screw hole; an monolithic shoulder-shank having a threadless inner diameter slightly larger than the diameter of the exterior threaded solid pin and at least one substantially radial threaded set screw hole; a pair of locking nuts having a threadless outer diameter and a threaded inner diameter operably compatable with the exterior threaded solid pin, wherein the shoulder and the monolithic shoulder-shank are capable of slidable engagement with the exterior threaded solid pin along the length of the exterior threaded solid pin to set a space slightly larger than a thickness of a work piece to be welded.
 8. The multi-shouldered friction stir welding tool according to claim 7 further comprises a lock nut threaded onto the exterior threaded solid pin into an abutting relationship with the shoulder.
 9. The multi-shouldered friction stir welding tool according to claim 7 further comprises a lock nut threaded onto the exterior threaded solid pin into an abutting relationship with the monolithic shoulder-shank.
 10. The multi-shouldered friction stir welding tool according to claim 7 further comprises substantially radial set screws to connect the shoulder and the monolithic shoulder-shank to the pair of locking nuts.
 11. A multi-shouldered friction stir welding tool comprising: an integral shank-pin unit having a plurality of pin portions on the shank-pin unit, wherein the plurality of pin portions for driving into a plurality of joints to perform a friction stir welding operation on the corresponding plurality of joints and, wherein a shank portion of the shank-pin unit is for attachment of an optional axial tension rod, a plurality of friction stir welding modules, each of the friction stir welding modules comprising: a pair of shoulders that is connected to the shank-pin unit where each shoulder has a distal end and a proximal end, where the proximal end of each shoulder faces the pin portion of the shank-pin unit, whereby the shoulder and pin(s) rotate in unison; and a pair of split collars or a pair of nuts that is connected to the shank-pin unit and faces the distal end of each shoulder; wherein the plurality of friction stir welding modules are connected to each other whereby the modules rotate in unison to simultaneously make a plurality of parallel welds.
 12. The multi-shouldered friction stir welding tool of claim 11 wherein the axial tension rod is disposed within the shank portion of the shank-pin unit.
 13. The multi-shouldered friction stir welding tool of claim 12 wherein the shank-pin unit contains a loading means for placing the axial tension rod in tension and the shank-pin in compression.
 14. The multi-shouldered friction stir welding tool of claim 11 wherein the shank-pin unit has threadless ends with at least two flats along the length of the shank-pin unit.
 15. The multi-shouldered friction stir welding tool of claim 11 wherein each shoulder has an opening to facilitate contact with threads on the shank-pin unit.
 16. The multi-shouldered friction stir welding tool of claim 11 further comprising each split collar has a threaded outer diameter and a threaded inner diameter that is connected to the shank-pin unit by threading the outer diameter of the collar onto threads on an inner diameter of the shoulder and threading the inner diameter of the collar onto threads on an outer diameter of the shank-pin unit.
 17. The multi-shouldered friction stir welding tool of claim 16 wherein each split collar is further tightened against or connected to the shank-pin unit by screws.
 18. The multi-shouldered friction stir welding tool of claim 11 further comprising each nut has a threaded outer diameter and a threaded inner diameter that is connected to the shank-pin unit by threading the outer diameter of the nut onto threads on an inner diameter of a shoulder and threading the inner diameter of the nut onto threads on an outer diameter of the shank-pin unit.
 19. The multi-shouldered friction stir welding tool of claim 18 wherein each nut is further tightened against or connected to the shank-pin unit by screws.
 20. The multi-shouldered friction stir welding tool of claim 19 wherein each nut is further connected to the shank-pin unit by jam nuts.
 21. The multi-shouldered friction stir welding tool of claim 11 wherein the shoulder may be a drive shank with an integrated shoulder.
 22. The multi-shouldered friction stir welding tool of claim 13 wherein the loading means for placing the axial tension rod in compression is a bearing disposed in a shank-pin unit end for disengaging and relieving the torque experienced by the pin portions of the shank-pin unit during the friction stir welding operation.
 23. The multi-shouldered friction stir welding tool of claim 16 wherein the distal end of the shoulder and the threaded outer diameter of the collar create a small pocket to prevent the plasticized material from flowing out of the joint.
 24. A method of friction stir welding a plurality of joints simultaneously comprising using at least one multi-shouldered friction stir welding tool of claim
 11. 25. The method of claim 24 wherein two multi-shouldered friction stir welding tools are simultaneously driven by a rotation-splitting transmission system.
 26. The method of claim 24 wherein two multi-shouldered friction stir welding tools are simultaneously driven by two synchronized servo controlled motors.
 27. The multi-shouldered friction stir welding tool of claim 11 wherein the shank-pin is made of a solid rod. 